1. Field of the Invention
The present invention relates to processes of producing glutamic acid compounds such as monatin, useful as production intermediates for sweetener or pharmaceutical products, as well as production intermediates therefore, and a novel important intermediate included in them. More specifically, the invention relates to a process of industrially efficiently producing the glutamic acid compounds, a process of producing production intermediates for use therefore and a novel intermediate included in them, and a process of producing optically active monatin, a process of producing production intermediates for use therefore, including a novel intermediate.
2. Description of the Background
Glutamic acid compounds such as monatin are compounds that are promising for use as sweetener or production intermediates for pharmaceutical products and the like. For example, it has been known that 4-hydroxy-4-(3-indolylmethyl)-2-aminoglutaric acid (3-(1-amino-1,3-dicarboxy-3-hydroxybutan-4-yl)indole, sometimes referred to as “monatin” hereinbelow) represented by the following formula (7′) in the (2S,4S) form is contained in the root of a plant Schlerochiton ilicifolius and has sweetness at a level several hundreds-fold that of sucrose (see JP-A-64-25757 (U.S. Pat. No. 4,975,298)).

In the specification, the term “monatin” is not limited to the (2S,4S) form naturally occurring but is used as the generic name of 4-hydroxy-4-(3-indolylmethyl)-2-aminoglutaric acid (3-(1-amino-1,3-dicarboxy-3-hydroxybutan-4-yl)indole) including the individual isomers in the forms of (2S,4S), (2S,4R), (2R,4S), and (2R,4R).
The following reports have been issued about processes of producing monatin (the following examples (2) to (5)) and protected monatin (the following example (1)).    (1) Process described in Tetrahedron Letters, 2001, Vol. 42, No. 39, pp. 6793-6796;
    (2) Process described in Organic Letters, 2000, Vol. 2, No. 19, pp. 2967-2970;
    (3) Process described in U.S. Pat. No. 5,994,559;
    (4) Process described in Synthetic Communications, 1994, Vol. 24, No. 22, pp. 3197-3211;
and    (5) Process described in Synthetic Communications, 1993, Vol. 23, No. 18, pp. 2511-2526 and U.S. Pat. No. 4,975,298 and U.S. Pat. No. 5,128,164;

Because any of the processes requires multiple steps, however, the industrial practice of the processes actually involves much difficulty. Some of the references shown above or other references (see T. Kitahara, et al., Japanese Agrochemical Association, the 2000-th Conference, Abstracts of Proceedings, 3B128β (p. 221)) describe about the examination of processes of producing optically active monatin. However, disadvantageously, the processes require multiple steps and involve very tough steps for industrial practice. Thus, it has been desired to develop an industrial process of efficiently producing glutamic acid compounds typically including monatin, particularly an industrial process of efficiently producing optically active monatin.